Somewhat means to a moderate degree. More than slightly, and less than very.
It is a hedging word and a formal one, which is why reports and academic writing use it far more than conversation does. Somewhat surprised, somewhat higher, somewhat of a problem. British English often uses it for understatement, so somewhat disappointing can mean a disaster. It usually sits directly before the adjective or adverb it softens. Rather and fairly do the same job in less formal registers.
1adverbsomewhatTo a moderate extent.
“The results were somewhat better than expected.”
From some + what.
Etymology from Wiktionary, CC BY-SA